The present invention relates to a guide rail employed in a linear guide device, and more particularly to an improvement of a guide rail fixing structure to increase the accuracy of motion of the slider of the linear guide device.
In general, a linear guide device, as shown in FIG. 7, comprises: a guide rail 1 which is extended axially; and a slide 2 which is movably mounted on the guide rail 1.
The guide rail 1 has two side surfaces 1b and 1b in each of which load ball rolling grooves 3 are formed in such a manner that they are extended axially (two load ball rolling grooves 3 in each of two side surfaces 1b and 1b in the case of FIG. 7). A body 2A of the slider 2 (hereinafter referred to as "a slider body 2A", when applicable) has right and left wings 4 and 4. Load ball rolling grooves (not shown) are formed in the inner surfaces of the wings 4 in such a manner that they are confronted with the load ball rolling grooves 3 of the guide rail, respectively. Furthermore, ball circulating paths are formed in the thick portions of the wings 4 in such a manner that they are connected to ends of the load ball rolling grooves thereby to form infinite circulation circles. A number of balls are rollingly fitted in the infinite circulation circles, so that the slider 2 is moved on the guide rail through the rolling of those balls.
A plurality of bolt holes 7 are formed in the guide rail 1 at predetermined intervals. The bolt holes 7 are through-holes extended from the top surface 1a of the body of guide rail 1 to the bottom surface 1c, and have counter bores 6 at the tops. Mounting bolts inserted into the bolt holes 7 are tightened to strongly push the bottom surfaces 6a of the counter bores 6 by the lower surfaces of the bolt heads, thereby to fixedly secure the guide rail, for instance, to a base stand. On the other hand, a driving structure to be guided such as a table is connected to the slider 2 so as to be moved along the guide rail 1.
In the guide rail 1 of the conventional linear guide device, as shown in FIG. 8, the depth h of the counter bore 6 of each of the bolt holes 7 (the distance between the top surface 1a of the guide rail 1 and the bottom 6a of the counter bore 6) is so determined that the head 8a of a hexagon socket head bolt 8 or a bolt cap 9 set on the bolt head 8a may not come above the top surface 1a of the guide rail 1. In other words, the depth h of the counter bore 6 of the bolt hole 7 is so determined as (1) to prevent the interference of the bolt head 8a or the bolt cap 9 with the slider 2 which is moved over the guide rail top surface 1a, and (2) to avoid the formation of recesses in the guide rail top surface 1a thereby to prevent the accumulation of chips therein.
The depth h of the bolt hole 7, which is determined only to prevent the interference of the bolt with the slider and to prevent the accumulation of dust on the guide rail, is substantially equal to the sum of the height of the head 8a of the hexagonal socket head bolt 8 and the thickness of the bolt cap 9. Hence, the distance A between the bottom 6a of the counter bore 6 of the bolt hole 7 and the guide rail bottom surface 1c is larger than the distance B between the guide rail bottom surface 1c and the lower end of the load rolling groove surface 3f (shaded in FIG. 8) of the load ball rolling groove 3 which is closet to the guide rail bottom surface 1c among the load ball rolling grooves 3 (A&gt;B).
When the mounting bolt 8 inserted into the bolt hole 7 thus designed is tightened, the bottom 6a of the counter bore 6 is strongly pushed by the lower surface of the bolt head 8a, so that the part of the guide rail which is located below the bottom 6a of the counter bore 6 is deformed. Because of this deformation, the load rolling groove surface 3f of the load ball rolling groove 3 is also deformed. The amount of deformation can be measured with the probe of a dial gauge set on the load ball rolling groove 3 which is located below the bottom 6a of the counter bore. That is, the amount of deformation is obtained as the difference between the values measured before and after the bolts are tightened. In the case of FIG. 8 in which only the part of the load rolling groove surface remote from the guide rail bottom surface 1c, is above in the bottom 6a of the counter bore 6, the amount of deformation of the load rolling groove surface 3f measured in the above-described manner was more than 1 .mu.m.
Recently, a linear guide device has been used for guiding the optical head of an optical disk driver for instance; that is, it is extensively employed in a field in which motion must be considerably high in accuracy to the order of microns (accuracies in the pitching, yawing and rolling of a slider which is moved on a guide rail). In this application of the linear guide device, the straightness of the load ball rolling grooves 3 of the guide rail is an important factor because it directly affects the accuracy of motion of the slider. Hence, in a linear guide device which must be high in the accuracy of motion, the deformation of the load ball rolling grooves which may be caused when the mounting bolts of the guide rail are tightened, becomes a serious problem.